Russian security services on Sunday said at least five militants were killed in a counter-terrorism operation in the southern Russian republic of Dagestan.

Security forces were responding to  attacks on a synagogue and an Orthodox church in Derbent, as well as a church and a police station in the state capital of Makhachkala, some 100 kilometers (62 miles) away.

Russian investigators said several civilians, including an Orthodox priest, and 15 police officers were killed in the "terrorist attacks." 

A Russian National Guard spokesperson said one of its officers had been killed in coastal Derbent and 12 more wounded.

Operation against gunmen in Derbent 'completed'

Russia's National Anti-terrorism Committee (NAC) said the "active phase of the counter-terrorist operation" in Derbent "is completed" but a standoff continued Makhachkala.

Gunfights between police and attackers had been earlier reported in both cities.

Russian state news agency TASS quoted anonymous law enforcement sources as saying, "the gunmen who carried out attacks in Makhachkala and Derbent are supporters of an international terrorist organization," without naming a specific organization.

There was no immediate claim of responsibility for the attacks. Authorities have opened a criminal investigation into an act of terrorism.

World Heritage synagogue ablaze

A fire was reported to have broken out after a gunfight at the synagogue, according to Interfax, citing the state Interior Ministry.

"The synagogue in Derbent is on fire," wrote Boruch Gorin, the chairman of the public council of Russia's Federation of Jewish Communities, on Telegram, "It has not been possible to extinguish the fire."

"The synagogue in Makhachkala has also been set on fire and burnt down," added Gorin.

Derbent is home to an ancient Jewish community whose synagogue is listed as a UNESCO World Heritage Site. The Russian Jewish Congress said on its website the Derbent synagogue was attacked about 40 minutes before evening prayers.

The rabbi of Makhachkala, Rami Davidov, said no one was killed or injured there.

Dagestan politicians point finger at Ukraine and West

Dagestan Governor Sergei Melikov called the attack an attempt to destabilize the impoverished, Muslim-majority region.

President Ramzan Kadyrov of neighboring Chechnya said, "What happened looks like a vile provocation and an attempt to cause discord between confessions." 

And Dagestan lawmaker Abdulkhakim Gadzhiyev leveled accusations against Ukraine and the West, claiming, "There is no doubt that these terrorist attacks are in one way or another connected with the intelligence services of Ukraine and NATO countries."

Still, Dagestan, which borders Chechnya, Georgia and Azerbaijan, has been a problem for Russian authorities for decades, with scores of police and civilians killed in clashes between Russia and militant Islamists.

Militants from the region are also known to have traveled to Syria in 2015 to fight with the Islamic State (IS) terror group, which later announced that it had opened a "franchise" in North Caucasus.

In May, Russia's FSB domestic security service said it arrested four individuals in connection to the massive attack on Moscow's Crocus City Concert Hall, for which IS claimed responsibility. 

js/dj,fb (dpa, Reuters, Interfax)